1. Field of the Invention
The present invention relates to a fluid expandable drum for building a tread and a radial tread ply band in a tire building machine and more particularly to a fluid expandable drum which includes an annular building surface which is movable in a radial direction upon expansion and contraction of the tube element. The tube element includes a radial ply and a radial ply band extending around the outer peripheral surface to increase the strength and resiliency of the outer peripheral surface to enable the building surface to decrease in diameter upon contraction of the tube element without the need of auxiliary springs.
2. Background of the Invention
Fluid expandable drums for building tires are well known in the art. An example of known tire building machinery is disclosed in the Henley U.S. Pat. No. 3,475,254; the Appleby, et al. U.S. Pat. No. 3,784,437; and the Iredell U.S. Pat. No. 2,614,951. Also, machines such as the NRM model R1016 Second Stage Radial Tire Building Machine have also been used in the art for the construction of tires.
Some known tire building machines generally utilize a tire building drum wherein a plurality of shoe means are utilized to form the tire building surface. The shoe means are biased outwardly in a radial direction upon expansion of a fluid expandable element. Spring means are provided to retract the shoes and decrease the diameter of the tire building surface upon contraction of the tube element. Such a construction is shown in the Henley U.S. Pat. No. 3,474,254 wherein the springs 160 are utilized to urge the gap shields 161 inwardly, and the Iredell U.S. Pat. No. 2,614,951 wherein springs 22 urge the segments 6 in an inwardly direction. The use of spring means to return the shoes and the building surface to their contracted position increases the cost, complexity and reliability of the known tire building mechanisms. Moreover, the use of such springs considerably increases the difficulties in replacing an expandable tube element in the tire building machine due to the fact that all of the spring means must be released before the tube element can be replaced.